Counterinvasion

Counterinvasion is a term used in military and strategic studies to describe the set of actions undertaken by a state or other actor to respond to an invasion. It encompasses defensive operations intended to halt the invading force, as well as counteroffensive maneuvers aimed at retaking territory and restoring sovereignty. The concept covers armed, political, economic, and diplomatic measures that together seek to deter further aggression, stabilize frontlines, and protect civilian populations.

Typical components include rapid mobilization of reserves, defense of critical infrastructure, air and sea denial operations, intelligence and surveillance, and the use of allied and external support to bolster defenses. Offensive countermeasures may involve staged counteroffensives, amphibious or airborne assaults, and strategic strikes designed to shift the balance of power. In irregular warfare, counterinvasion can also involve sustained resistance, guerrilla activity, and information campaigns to undermine the aggressor's legitimacy.

Historical usage of the term is varied; many military historians describe the Allied counteroffensives in World War II, such as the campaigns in Western Europe in 1944–1945, as examples of counterinvasion dynamics, where defenders initiated operations to push back invading forces and retake territory. In modern conflicts, counterinvasion considerations often intersect with anti-access/area-denial strategies and international diplomacy aimed at securing sanctions, arms support, and multinational coalitions.

Legal and ethical aspects center on the principles of jus ad bellum and jus in bello, including proportionality, necessity, and distinction between military targets and civilians. The term remains somewhat fluid and is frequently used descriptively rather than as a formal doctrine, varying across national doctrines and scholarly analysis.